Method and apparatus for coding in a telecommunications system

ABSTRACT

First and second transmission links are established with a remote station. An information signal is encoded to provide an encoded information signal having more bits than the information signal. First and second transmission signals are provided wherein each transmission signal has bits selected from the encoded information signal. Each of the first and second transmission signals is transmitted to the remote station by way of a respective one of the first and second transmission links. The remote station receives and combines the first and second transmission signals transmitted by the remote station to provide a combined encoded signal. The combined encoded signal is decoded by the remote station to provide the information signal. The first and second transmission links can be formed between the remote station and a single base station or between the remote station and two separate base stations.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

[0001] The present Application for Patent is a Continuation and claimspriority to patent application Ser. No. 10/386,998 entitled “A Methodand Apparatus for Coding in a Telecommunications System” filed Mar. 11,2003, now allowed, which is a Continuation of U.S. Pat. No. 6,560,292entitled “Method for Coding in a Telecommunications System” filed Apr.7, 2000 and issued May 6, 2003, all assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

[0002] 1. Field

[0003] The present invention relates to communications in general and,in particular, to improving the transmission of information signals in acommunications system.

[0004] 2. Background

[0005] The quality of a communication link over a noisy channel dependson the energy to interference noise ratio Eb/No of the signal. Toachieve a required bit error rate over the communication link, aparticular Eb/No is required. The bit error rate is a function ofseveral parameters including channel propagation characteristics. Inorder to reach the target Eb/No a transmitter must transmit a signalwith sufficient power. In practice, communication systems of this typeare power limited. In power limited systems the transmitter cannotnecessarily transmit the amount of power required to maintain a desiredbit error rate. In CDMA systems, the sum of the power required by eachlink in the system determines the overall capacity of the system. Thus,it is desirable for each communication link to require the lowest Eb/Nopossible.

[0006] In order to decrease the required Eb/No in CDMA systems, the datato be transmitted can be encoded. Many different encoders are known inthe art. For example, conventional convolutional and turbo encoders aresuitable for this purpose. All of the suitable encoders perform the samebasic task of creating redundancy in the encoded information signal. Insuch encoding techniques, each encoded bit is a function of a pluralityof input bits.

[0007] For example, the encoder system 1 of FIG. 1 can be used toprovide a redundant encoded signal suitable for use in decreasing therequired Eb/No in a CDMA communication system. The rate R encoder 4 ofthe encoder system 1 receives a stream of k information bits 2 andoutputs a larger stream 6 of n coded bits wherein R is the code rate.The code rate R is the ratio of the number of information bits k perunit of time to the number of coded bits n per unit of time. Thus R=k/n,and n=k/R. The n bits of coded bit stream 6 at the output of the rate Rencoder 4 can be transmitted over the transmission channel 8. A rate Rdecoder 12 performs a decoding operation that is the inverse of theoperation performed by the rate R encoder 4. That is, the rate R decoder12 converts the received n coded bits 10 into k information bits 14 thatare substantially equivalent to the k information bits 2 that were inputto the rate R encoder 4. In CDMA systems, typically the rate R=½ or R=⅓.

[0008] It is known that for similar encoding techniques a lower coderate R permits a lower Eb/No to obtain the same bit error rate (where itis understood that ⅓ is a “lower” rate than ½). However, thisimprovement in performance becomes negligible when the code rate Rbecomes too low. Typically little further improvement occurs below R=⅙.Furthermore, since the number of encoded bits increases as the code rateR gets smaller it is usually not desirable or even possible to transmitthe large number of coded bits required for code rates lower than R=⅙.Typically, code rates of ½ and ⅓ are preferred.

[0009] Although the use of a lower code rate is desirable, because itwould lower the required Eb/No in a CDMA communication system, it isdeemed undesirable to use a lower code rate if doing so would have anoverall adverse effect, such as lowering system capacity.

[0010] Lower code rates generate more bits for transmission than dohigher code rates. For example, if the code rate on a system weredecreased from ½ to ¼, it would double the number of coded bits neededto be transmitted by the system. Thus, bandwidth between the remotestation and the base station would need to be doubled in order tosupport such a decrease in code rates.

[0011] In a CDMA system, one could double the effective bandwidth on theforward link by halving the length of the Walsh codes used fororthogonally spreading the encoded bit stream. For example, by halvingthe length of the Walsh codes used in a CDMA system from 64 bits to 32bits, a given data stream could be transmitted over the forward link inhalf the number of coded bits. Although decreasing the Walsh code lengtheffectively increases the bandwidth between the remote station and thebase station, it is undesirable to decrease the Walsh code lengthbecause doing so decreases the pool of Walsh codes. As is well known inthe art, a decreased pool of Walsh codes decreases the number of usersthat the system can support. When a system has allocated all of itsWalsh codes to users, no more users can be added to the system becausethe system is said to be “code limited”.

[0012] Since the number of spreading codes in a system is limited, theadvantages of any gain achieved with a low code rate R can be offset bythe disadvantage of the use of additional spreading codes. Thus,although decreasing the code rate R used by each user in a CDMAcommunication system improves the required Eb/No per user, it can alsolimit the number of users by creating a shortage of spreading codes.Although there exists ways of creating more spreading codes, such as byusing quasi-orthogonal functions or by using multiple scrambling (PN)codes, these techniques are used as a last resort because theysignificantly increase the overall interference level in the system.

[0013] Besides being code limited, a system may be limited in the numberof users it can support at a given time due to limits in the amount ofpower that the base station can transmit. Transmitting more power thanis allowed will cause interference that cannot be tolerated by theadjacent cells. When a new user is added to the system, the amount ofpower that is transmitted by the base station will increase. Becausethere is a limit on the amount of power that the base station cantransmit, the number of users may be limited by the total amount ofpower that can be transmitted. Therefore, even if there are additionalspreading codes available, the number of users will be limited by theamount of power that can be transmitted by the base station. When a basestation is limited in the number of users it can support at a given timedue to power transmission limitations, the system is said to be “powerlimited.”

[0014] To improve the performance of a telecommunicationsystem—performance which is usually measured in Erlangs, bits perseconds, or number of users—it is necessary to take into account bothcode limitations and power limitations. What is desired is a way toincrease the system performance of a telecommunications system, oftenmeasured in the number of users that a telecommunications system cansimultaneously support, by taking into account the fact that the systemis both code limited and power limited.

SUMMARY

[0015] A method is taught for improving the transmission of informationsignals in a communications system having a base station and a remotestation. First and second transmission links are established with theremote station. A base station information signal is encoded to providean encoded information signal having more bits than the informationsignal. First and second transmission signals are provided wherein eachtransmission signal has bits selected from the encoded informationsignal. The first and second transmission signals are each transmittedto the remote station by one of the first and second transmission links,respectively. The remote station receives and combines the first andsecond transmission signals transmitted by the remote station to providea combined encoded signal. The combined encoded signal is decoded by theremote station to provide the information signal. The first and secondtransmission links can be formed between the remote station and a singlebase station or between the remote station and two separate basestations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features, objects, and advantages of the present inventionwill become more apparent form the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters identify corresponding elements throughout and wherein:

[0017]FIG. 1 shows a conventional information bit stream encoder systemsuitable for encoding signals in a wireless communications system;

[0018]FIG. 2 shows a block diagram representation of a method fortransmitting information in a wireless communications system;

[0019]FIG. 3 shows a code generator system using puncturing of a lowercode signal to provide a required signal;

[0020]FIG. 4 shows a wireless communications system wherein the methodof the present invention can be advantageously applied; and

[0021]FIG. 5 shows an alternative block diagram representation of amethod for transmitting information in a wireless communications system.

[0022]FIG. 6 is a block diagram showing a simplified illustration of aremote station.

[0023]FIG. 7 is a block diagram of a portion of a digital demodulatorand a wash dispreading unit that can be used to receive data in thereceived data detection mode of the present embodiments.

[0024]FIG. 8 is an exemplary embodiment of a dot product.

[0025]FIG. 9 is a block diagram of a portion of a digital demodulatorand a wash dispreading unit that can be used to receive data in thereceived data detection mode of the present embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0026]FIG. 2 is a block diagram of a signal transmission method 240 inaccordance with one embodiment of the present invention. In signaltransmission method 240, a base station information bit stream to betransmitted to a remote station is received for encoding in block 242.The process then moves to block 244.

[0027] In block 244 the information bit stream is encoded into a lowerrate encoded bit stream to decrease the required Eb/No needed totransmit the bits to a remote station (as mentioned earlier, a lowercode rate generates more bits than a higher coderate but requires lesstransmit power to achieve the same quality of service). In an exemplaryembodiment, the encoder is a rate ¼ turbo encoder. In alternateembodiments, various encoder rates and types can be used. In anexemplary embodiment, the encoder has a property such that the odd bitsof the ¼ rate encoded bit stream make up a ½ rate encoded bit stream,and the even bits make up a second ½ rate encoded bit stream. In otherwords, bits 1, 3, 5, etc. make up one ½ rate encoded bit stream and bits2, 4, 6, etc make up a separate ½ rate encoded bit stream. All of thebits, however, comprise the ¼ rate encoded bit stream. In theaforementioned embodiment, the ¼ rate encoded bit stream is the lowerrate encoded bit stream referenced earlier. In alternate embodiments thebits are arranged such that a different combination of the bits makes upthe two ½ rate streams (e.g., the first n/2 bits comprise one ½ rateencoded bit stream, while the second n/2 bits comprise a second ½ rateencoded bit stream). In the above exemplary embodiments, the fact thatthe lower rate encoded bit stream comprises at least one standard bitencoded bit stream allows the encoder to produce only a single bitstream that could be used for transmission on two channels as laterdescribed in reference to block 250 and which also could have a portionof it used for transmission on a single channel in block 252. In yetanother alternate embodiment, the encoder produces two separate bitstreams, one encoded at a lower rate and one encoded at a standard rate(e.g., ¼ rate and ½ rate, respectively). In this alternate embodiment,the lower rate encoded bit stream need not be comprise two standard rateencoded bit streams. In this embodiment, the lower rate encoded bitstream would be used for transmission when the process branches to block250 and the separate standard rate encoded bit stream would be used fortransmission when the process branches to block 252.

[0028] The process then moves from block 244 to decision block 246.Block 246 is representative of a decision block wherein it is determinedwhether a single standard rate encoded bit stream should be transmittedon a single channel or whether a lower rate encoded bit stream should betransmitted in portions over two channels. Any parameter(s) within aCDMA communication system can be used as the basis of the decision indecision block 246. The only criterion for selecting a parameter for usein decision block 246 is whether the parameter can be used to optimizethe communication system in some way. Thus, the quality determinationmade in decision block 246 can be made based on any one of a largenumber of different quality factors. A straightforward way to make thedecision is to have the transmitter recognize that it is transmitting ata high power level (for example, recognizing that more than 10% of thebase station's transmit power capacity is being used on any given remotestation), and that it should switch from one transmit stream to twotransmit streams.

[0029] In one embodiment, in block 246, it is determined whether theamount of transmit power that would be utilized to transmit the data asa single standard rate encoded bit stream is above a predeterminedthreshold. The power level of the transmission is increased as necessaryin order to maintain a desired bit error rate, but the power level cannot be increased without limit. Thus, in decision block 246 adetermination is made as to whether “excessive” transmission power isrequired to maintain the bit error rate. If the transmission power isdeemed “excessive,” then the process proceeds to block 250, wherein thelower rate encoded bit stream is transmitted on two channels.

[0030] In one embodiment, in decision block 246 it is also checkedwhether the number of spreading codes presently available is above apre-determined first threshold value. In such a case, not only must“excessive” power be determined, but also the number of availablespreading codes must be above the first threshold value in order for theprocess to move to block 250. The first threshold value is zero in oneembodiment, meaning that there must be at least one available spreadingcode. This check is done because, although it is desirable to reducepower by transmitting data over two channels, a code needs to beavailable to allocate to the secondary channel.

[0031] In one embodiment, it is determined in decision block 246 whetherthe remote station is in soft-handoff or in softer-handoff. As is knownin the art, when a remote station is in soft-handoff or softer-handoff,a remote station has communication channels open with more than one cellsite sector. Hereinafter, soft-handoff shall be used to refer to bothsoft-handoff and softer-handoff. If it is determined that a remotestation is in soft-handoff, then the process moves to block 250. Thereason the process moves to block 250 is as follows. In a conventionalsystem, each sector would transmit the same standard encoded bit streamusing one channel (Walsh code) per sector. Using the method of thepresent embodiment uses no extra channels in this instance, because onlytwo channels are needed, and they would have been used in theconventional system during soft-handoff anyway. Proceeding to block 250thus does not use any extra channels, yet it yields the gain describedin reference to block 250 below. Namely, less power can be used whentransmitting a lower encoded rate bit stream than when transmitting astandard encoded rate bit stream. This relationship holds true even whenthe same standard encoded bit stream is transmitted on multiplechannels, as it is in a conventional system while a remote station is insoft-handoff. Thus, due to the increased system performance from thepower savings that can be obtained, the process moves to block 250 whenthe remote station is in soft-handoff.

[0032] In one embodiment a pre-determined second threshold value can beused in block 246 to determine whether or not to move to block 250irrespective of whether or not it is determined that “excessive” poweris being used to transmit to the remote station. In such a case, if thenumber of available spreading codes is above the second threshold value,thus indicating that using an extra code for the call in question wouldlikely not cause a shortage of codes that would reduce system capacity,then the process would proceed to block 250, irrespective of whether theamount of power being used to transmit to the remote station isexcessive. In this case, although the transmitter's power might not beexcessive, reducing the transmitter's power by any amount will stillbenefit the wireless system because it reduces the likelihood ofinterfering with other cells. Because there is presently no shortage ofspreading codes, and the likelihood is low that there will be a shortageof spreading codes anytime soon (as determined by comparing the numberof available codes with a second threshold value), it is beneficial touse one of the spreading codes to reduce transmit power, thus increasingsystem performance.

[0033] One skilled in the art will appreciate that decision block 246can use any combination of the above embodiments, or it can use anyother embodiments that can determine whether transmitting data to aparticular remote station across two channels will optimize thecommunication system, to decide whether or not to proceed to block 250in which the lower rate encoded bit stream is transmitted on twochannels. One simple embodiment that can be used in decision block 246is to check the setting of a flag, variable, or register, to determinewhether or not the communication system will benefit from transmittingdata to a particular remote station across two channels. This is usefulin a communication system wherein a complex determination is first madethat two channels should be used for transmission, after which a singleindicator bit, or a message containing multiple bits, both of which arehereinafter referred to as an indicator message, is sent to the remotestation to indicate that a lower rate encoded bit stream will betransmitted on two channels at a predetermined point in time in thefuture. A flag is then set in the telecommunication system to indicatethat future bit streams should be transmitted across two channels at apredetermined point in time. In such a case, just a flag would need tobe checked in block 246.

[0034] If, in block 246, it is determined that the communication systemwill benefit from transmitting data to a particular remote stationacross two channels, the process proceeds to block 250. Otherwise, theprocess proceeds to block 252.

[0035] In block 250, the telecommunications system uses a mode ofcommunication with the base station such that a first portion of thelower rate encoded bit stream is transmitted on a primary channel, whilea second portion is transmitted on a secondary channel. In oneembodiment, the two separate standard rate encoded bit streams that makeup the lower rate encoded bit stream are transmitted over a primary andsecondary channel. For example, if the lower rate encoded bit stream isa ¼ rate bit stream comprising both a standard ½ rate encoded bit streamin its odd bits and a standard ½ rate encoded bit stream in its evenbits, then the odd bits of the stream would be transmitted over aprimary channel and the even bits would be transmitted over a secondarychannel. In the aforementioned embodiment the portions transmitted areof equal length. However, the present invention is not limited to suchan embodiment. In alternate embodiments, portions of varying length canbe transmitted on multiple channels. For instance, an encoded bit streamcould have one third of its bits transmitted on a primary channel andthe remaining two thirds of its bits transmitted on a secondary channel.

[0036] The use of two channels rather than one results in a higher gainwithin the communication system. The second transmission channel can beestablished when needed or it can already be in use.

[0037] After the encoded bit streams are formed for each channel, eachbit stream is transmitted in accordance with traffic channelrequirements for the specific system at hand. For example, as is knownto one skilled in the art, in a cdma2000 system the forward linkchannel's encoded bit stream is interleaved, covered with a Walsh code,spread with a PN sequence, and digitally modulated using QuadraturePhase Shift Keying (QPSK). It will be understood that performing signaltransmission in this manner requires a base station to use two Walshcodes rather than one, because two channels are being used instead ofone. Furthermore, it will be understood that when performing signaltransmission is this manner, the transmit power of each of thetransmission channels of block 250 can be less than one half thetransmit power needed to maintain a desired bit error rate had only asingle channel been used. Thus, the peak power requirement fortransmitting the encoded information signal is reduced by more than onehalf.

[0038] When transmitting data in this mode, the communication systemneeds to indicate to the remote station that it needs to begin receivingbit streams at a lower code rate, wherein the bit stream are transmittedin portions amongst multiple channels. As stated in relation to block246, this indication can be transmitted as an indicator message prior tothe point in time at which data transmissions in this mode begin. Or,alternatively, one or more indicator bits can be transmitted atsubstantially the same time as that in which the bit streams aretransmitted in block 250. For instance, there could be a separatechannel that the mobile monitors just before, or at the beginning of thereception of a bit stream to determine whether to receive the bit streamacross two channels. This would be of value in a telecommunicationssystem in which several remote stations share a dedicated secondaryWalsh code, and wherein a given remote station can begin decoding asecond channel with that dedicated Walsh code shortly after receiving anindicator bit instructing it to do so.

[0039] The process then returns to block 242.

[0040] Returning to block 246, if it is determined that thecommunication system will not benefit from transmitting data to aparticular remote station across two channels, the process proceeds toblock 252. In block 252, a standard rate encoded bit stream istransmitted over a primary channel. In one embodiment, one in which theencoder produces a single lower rate encoded bit stream, the standardrate encoded bit stream to be transmitted is extracted from the lowerrate encoded bit stream. For example, the odd bits could be extracted toform the standard rate encoded bit stream. In an alternate embodiment,one in which the encoder produces both a lower rate encoded bit streamand a standard rate encoded bit stream, no extraction of bits isnecessary. In such an embodiment, the standard rate encoded bit streamis simply transmitted on a primary channel. The process then returns toblock 242.

[0041] One skilled in the art will appreciate that in alternateembodiments the blocks need not be in the order they appear in FIG. 2.For instance, one skilled in the art will appreciate that in onealternate embodiment, block 244 and block 246 could be reversed, suchthat the decision of whether to transmit a lower rate encoded bit streamis made prior to the generation of the encoded bit stream. Oneembodiment in which the decision of whether to transmit a lower rateencoded bit stream is made prior to the generation of the encoded bitstream is shown in FIG. 5.

[0042]FIG. 5 is an alternative block diagram of a signal transmissionmethod 1240 in accordance with one embodiment of the present invention.In signal transmission method 1240, a base station information bitstream to be transmitted to a remote station is received for encoding inblock 1242.

[0043] The process then moves from block 1242 to block 1246. Block 1246is representative of a decision block wherein it is determined whether asingle standard rate encoded bit stream should be transmitted on asingle channel or whether a lower rate encoded bit stream should betransmitted in portions over two channels. Any parameter(s) within aCDMA communication system can be used as the basis of the decision indecision block 1246. The only criterion for selecting a parameter foruse in decision block 1246 is whether the parameter can be used tooptimize the communication system in some way. Thus, the qualitydetermination made in decision block 1246 can be made based on any oneof a large number of different quality factors. A straightforward way tomake the decision is to have the transmitter recognize that it istransmitting at a high power level, and that it should switch from onetransmit stream to two transmit streams.

[0044] In one embodiment, in block 1246, it is determined whether theamount of transmit power that would be utilized to transmit the data asa single standard rate encoded bit stream is above a predeterminedthreshold. The power level of the transmission is increased as necessaryin order to maintain a desired bit error rate, but the power level cannot be increased without limit. Thus, in decision block 1246 adetermination is made as to whether “excessive” transmission power isrequired to maintain the bit error rate. If the transmission power isdeemed “excessive,” then the process proceeds to block 12441 wherein alower rate encoded bit stream is generated, and subsequently transmittedon two channels in block 1250. This occurs because a base station thatis transmitting signals to a remote station at an excessively high powerlevel can significantly lower its transmit power level by transmittingthe signal at a lower code rate over two channels. Due to thesignificant decrease in transmit power achieved, system capacity islikely greater in this case, even with the loss of a Walsh code, than ifthe transmit power to this remote station remained excessive and theWalsh code had been saved.

[0045] In one embodiment, in decision block 1246, it is also checkedwhether the number of spreading codes presently available is above apre-determined first threshold value. In such a case, not only must“excessive” power be determined, but also the number of availablespreading codes must be above the first threshold value in order for theprocess to move to block 12441. The first threshold value is zero in oneembodiment, meaning that there must be at least one available spreadingcode. This check is done because, although it is desirable to reducepower by transmitting data over two channels, a code needs to beavailable to allocate to the secondary channel.

[0046] In one embodiment, in decision block 1246, it is determinedwhether the remote station is in soft-handoff or in softer-handoff. Asis known in the art, when a remote station is in soft-handoff orsofter-handoff, a remote station has communication channels open withmore than one cell site sector. Hereinafter, soft-handoff shall be usedto refer to both soft-handoff and softer-handoff. If it is determinedthat a remote station is in soft-handoff, then the process moves toblock 12441 wherein the lower rate encoded bit stream is generated, andsubsequently transmitted in block 1250, as described below. The reasonthe process moves to block 12441 is as follows. In a conventional systemeach sector would transmit the same standard encoded bit stream usingone channel (Walsh code) per sector. Using the method of the presentembodiment uses no extra channels in this instance, because only twochannels are needed, and they would have been used in the conventionalsystem during soft-handoff anyway. Proceeding to block 12441, andsubsequently to block 1250, thus does not use any extra channels (Walshcodes), yet it yields the gain described in reference to blocks 12441and 1250. Namely, less power can be used when transmitting a lowerencoded rate bit stream than when transmitting a standard encoded ratebit stream. This relationship holds true even when the same standardencoded bit stream is transmitted on multiple channels, as it is in aconventional system while a remote station is in soft-handoff. Thus, dueto the increased system performance from the power savings that can beobtained, the process moves to block 12441, and subsequently to block1250, when the remote station is in soft-handoff.

[0047] In one embodiment a pre-determined second threshold value can beused in block 1246 to determine whether or not to move to block 12441irrespective of whether or not it is determined that “excessive” poweris being used to transmit to the remote station. In such a case, if thenumber of available spreading codes is above the second threshold value,thus indicating that using an extra code for the call in question wouldlikely not cause a shortage of codes that would reduce system capacity,then the process would proceed to block 12441, irrespective of whetherthe amount of power being used to transmit to the remote station isexcessive. In this case, although the transmitter's power might not beexcessive, reducing the transmitter's power by any amount will stillbenefit the wireless system because it reduces the likelihood ofinterfering with other cells. Because there is presently no shortage ofspreading codes, and the likelihood is low that there will be a shortageof spreading codes anytime soon (as determined by comparing the numberof available codes with a second threshold value), it is beneficial touse one of the spreading codes to reduce transmit power, thus increasingsystem performance.

[0048] One skilled in the art will appreciate that decision block 1246can use any combination of the above embodiments, or it can use anyother embodiments that can determine whether transmitting data to aparticular remote station across two channels will optimize thecommunication system, to decide whether or not to proceed to block 12441in which the lower rate encoded bit stream is transmitted on twochannels. One simple embodiment that can be used in decision block 1246is to check the setting of a flag, variable, or register, to determinewhether or not the communication system will benefit from transmittingdata to a particular remote station across two channels. This is usefulin a communication system wherein a complex determination is first madethat two channels should be used for transmission, after which afterwhich an indicator message is sent to the remote station to indicatethat a lower rate encoded bit stream will be transmitted on two channelsat a predetermined point in time in the future. A flag is then set inthe telecommunication system to indicate that future bit streams shouldbe transmitted across two channels at a predetermined point in time. Insuch a case, just a flag would need to be checked in block 1246.

[0049] If, in block 1246, it is determined that the communication systemwill benefit from transmitting data to a particular remote stationacross two channels, the process proceeds to block 12441. Otherwise, theprocess proceeds to block 12442.

[0050] In block 12441 the information bit stream is encoded into a lowerrate encoded bit stream to decrease the required Eb/No needed totransmit the bits to a remote station (as mentioned earlier, a lowercode rate generates more bits than a higher code rate). In an exemplaryembodiment, the encoder is a rate ¼ turbo encoder. However, it should benoted that various encoder rates and types can be used. In an exemplaryembodiment, the encoder has a property such that the odd bits of the ¼rate encoded bit stream make up a ½ rate encoded bit stream, and theeven bits make up a second ½ rate encoded bit stream. In other words,bits 1, 3, 5, etc. make up one ½ rate encoded bit stream and bits 2, 4,6, etc make up a separate ½ rate encoded bit stream. All of the bits,however, comprise the ¼ rate encoded bit stream. In the aforementionedembodiment, the ¼ rate encoded bit stream is the lower rate encoded bitstream referenced earlier. In alternate embodiments the bits arearranged such that a different combination of the bits makes up the two½0 rate streams (e.g., the first n/2 bits comprise one ½ rate encodedbit stream, while the second n/2 bits comprise a second ½ rate encodedbit stream). In alternate embodiments the lower rate encoded bit streamis not comprised of two standard rate encoded bit streams.

[0051] The process then moves to block 1250.

[0052] In block 1250, a first portion of the lower rate encoded bitstream is transmitted on a primary channel, while a second portion istransmitted on a secondary channel. In one embodiment, the two separatestandard rate encoded bit streams that make up the lower rate encodedbit stream are transmitted over a primary and secondary channel. Forexample, if the lower rate encoded bit stream is a ¼ rate bit streamcomprising both a standard ½rate encoded bit stream in its odd bits anda standard ½rate encoded bit stream in its even bits, then the odd bitsof the stream would be transmitted over a primary channel and the evenbits would be transmitted over a secondary channel. In theaforementioned embodiment the portions transmitted are of equal length.However, the present invention is not limited to such an embodiment. Inalternate embodiments, portions of varying length can be transmitted onmultiple channels. For instance, an encoded bit stream could have onethird of its bits transmitted on a primary channel and the remaining twothirds of its bits transmitted on a secondary channel.

[0053] The use of two channels rather than one results in a higher gainwithin the communication system. The second transmission channel can beestablished when needed or it can already be in use. Additionally, morethan one remote station operating according to transmission method 1240can share a secondary channel.

[0054] It will be understood that performing signal transmission in thismanner requires a base station to use two Walsh codes rather than one.Furthermore, it will be understood that when performing signaltransmission is this manner, the transmit power of each of thetransmission channels of block 1250 can be less than one half thetransmit power needed to maintain a desired bit error rate had only asingle channel been used. Thus, the peak power requirement fortransmitting the encoded information signal is reduced by more than onehalf.

[0055] When transmitting data in this mode, the communication systemneeds to indicate to the remote station that it needs to begin receivingbit streams at a lower code rate, wherein the bit stream are transmittedin portions amongst multiple channels. As stated in relation to block1246, this indication can be transmitted as an indicator message priorto the point in time at which data transmissions in this mode begin. Or,alternatively, one or more indicator bits can be transmitted atsubstantially the same time as that in which the bit streams aretransmitted in block 1250. For instance, there could be a separatechannel that the mobile monitors just before, or at the beginning of thereception of a bit stream to determine whether to receive the bit streamacross two channels. This would be of value in a telecommunicationssystem in which several remote stations share a dedicated secondaryWalsh code, and wherein a given remote station can begin decoding asecond channel with that dedicated Walsh code shortly after receiving anindicator bit instructing it to do so.

[0056] The process then returns to block 1242.

[0057] Returning to block 1246, if it is determined that thecommunication system will not benefit from transmitting data to aparticular remote station across two channels, the process proceeds toblock 12442. In block 12442, a standard rate encoded bit stream isgenerated. In one embodiment, only a standard rate encoded bit stream isgenerated in block 12442. In an alternate embodiment, a lower rateencoded bit stream is first generated, and then a standard rate encodedbit stream is extracted from bits of the lower rate encoded bit stream.The process then moves to block 1252, wherein the standard rate encodedbit stream is transmitted over a primary channel. The process thenreturns to block 1242.

[0058]FIG. 3 illustrates a code generator system 20. Encoder systemssuch as code generator system 20 can be used to generate a code having arequired code rate R by extracting a portion of the output of a lowerrate code. For example, in code generator system 20, two sets of ½ ratecoded bit streams are provided by using a ¼ rate encoder 24. Informationbits 22 of encoder system 20 are applied to ¼ rate encoder 24 to produceR=¼ coded bit stream 26. In an exemplary embodiment the odd bits of theoutput make up a ½ rate coded bit stream and the even bits make up asecond ½ rate coded bit stream. Thus, when the portion of odd bits isextracted from R=¼ coded bit stream 26, a first R=½ coded bit stream 28is generated. Likewise, when the portion of even bits is extracted fromR=¼ coded bit stream 26, a second R=½ coded bit stream 30 is generated.Thus a code rate R=½ can be generated by extracting a predefined set ofbits from the output of R=¼ rate encoder 24. A remote station receivingboth R=½ coded bit stream 28 on a primary channel and R=½ coded bitstream 30 on a secondary channel can combine the bits together intotheir correct predefined positions and decode the full R=¼ coded bitstream 26. It is understood by one skilled in the art that in alternateembodiments encoder system 20 could comprise an encoder that encodes ata different code rate R and/or that generates a coded bit stream ofhigher code rates in patterns other than a 2R code rate bit streamlocated in the odd bits and a 2R code rate bit stream located in theeven bits.

[0059] Thus code generator system 20 can be used to generate a lowerrate encoded bit stream containing a first and second portion of bits,each of which comprises a first standard rate encoded bit stream and asecond standard rate encoded bit stream, respectively. The firststandard rate encoded bit stream and the second standard rate encodedbit stream can be transmitted to the remote station where they can becombined and decoded. Using this method of transmission permits all ofthe information of the unencoded information bit stream to be decoded bythe remote station from a single one of the two encoded signals receivedon one of the two channels used for transmission. This permits thereceiver to decode the signal even if one of the transmissions is notreceived. However, a decoding performed using only one of the encodedsignals is less robust than a decoding performed using both encodedsignals. Therefore, both encoded signals should be used if they areavailable.

[0060] Code combining methods suitable for use in combining the encodedstreams are well known in the art. It is understood by one skilled inthe art that if a remote station receives only a subset of the encodedstreams provided in the generalized case it can still decode theinformation bits, with reduced decoding performance. It will beunderstood by one skilled in the art that encoders of other rates, R,can be used in other embodiments.

[0061] In FIG. 4, there is shown CDMA communication system 30. CDMAcommunication system 30 includes base stations 32, 34 located inadjacent sectors S1 and S2 and remote stations 36, 38. In CDMAcommunication system 30 remote stations 36, 38 suffer the worsttransmission interference when they are at the edge of a cell. The majorreason for this is that the propagation loss is largest when they arefarthest from base stations 32, 34. Additionally, remote stations 36, 38are closest to interfering cells at this point. It is thereforedesirable to improve the decoding results when remote stations 36, 38are at the edge of a cell.

[0062] Conventionally a communication link is established between remotestations 36, 38 and all nearby sectors. Remote stations 36, 38 receivethe same coded bits from each of the nearby sectors and combine them inpower, in a conventional system. This process is referred to as softhandoff for sectors belonging to different cells and softer handoff forsectors in the same cell. The method of the present embodiments can beadvantageously applied to both soft and softer handoff.

[0063] In the method of the present embodiments, in the case of softhandoff each sector encodes the same information bits. However, theencoding is not necessarily performed with the same code. In the methodof the present embodiments, remote station 36 can initiate a call whenit is located well within an initial sector S₁. In this case, sector S₁transmits the information bits encoded with a code C₁ of rate R₁ overcommunication link 33. Remote station 36 can then move to the boundarybetween the original sector S₁ and another sector S₂. In FIG. 4, remotestation 36 is at the boundary between sector S₁ and another sector S₂.At this point, remote station 36 goes into soft handoff with the twosectors. In one embodiment of the invention, sector S₂ transmits thesame information bits encoded with a code C₂ of rate R₂ over acommunication link 35. If the R₁ and R₂ codes are chosen correctly,remote station 36 can combine the stream of coded bits from sector S₁with the coded bits from sector S₂ in such a way that it obtains theequivalent of information bits coded with a code of rate1/((1/R₁)+(1/R₂)). For example, if code rate R₁=½ and code rate R₂=½,the remote station could combine the coded bit streams into a singlecoded bit stream of R=¼ in the method of the present embodiments.

[0064] Remote station 36 has to correctly combine the bits. In theexample of a lower rate coding scheme wherein the odd bits make up afirst standard rate encoded bit stream and the even bits make up asecond standard rate encoded bit streams, the odd bits will betransmitted from one sector and the even bits will be transmitted fromanother sector. The remote station needs to know a priori which sectoris transmitting the odd bits and which is transmitting the even bits sothat it can properly assemble the standard rate encoded bit stream fromthe two lower rate encoded bit streams. In one embodiment of theinvention, a handoff direction message, presently used to instruct aremote station to enter soft handoff with a particular sector, willcontain one or more bits that indicate to the remote station how tocombine the bits from each sector.

[0065] In one embodiment, a separate message of one or more bits in thehandoff message (e.g., extended handoff direction message in cdma2000)informs the remote station how the bits from a particular channel on aparticular sector should be combined with the bits from other channelson other sectors. For instance, if a system were to use the odd bit/evenbit method of encoding, as described earlier, a base station could senda handoff redirection message to remote station 36 using one bit in thatmessage to tell the remote station whether the bits from Sector S2should be treated as the odd bits or the even bits in the stream, andusing one bit telling the remote station how the bits from Sector S2should be treated.

[0066] In another embodiment, the bits are ordered in a pre-determinedfashion in accordance with the base station identifiers associated withthe channels of the communication with a remote station. For example, inone embodiment a system could be designed wherein when a remote stationis in soft handoff, the odd bits of a lower rate encoded bit stream willbe transmitted from the base station involved in the communication thathas the lowest base station identifier, while the even bits of the lowerrate encoded bit stream will be transmitted from the other base stationsinvolved in the communication. For instance, if a remote station were ina soft-handoff with base stations having identifiers of B and C (notshown), base station B would transmit the odd bits of a lower rateencoded bit stream while base station C would transmit the even bits.

[0067] If the remote station subsequently goes into a three-way handoff,with base stations A, B, C (not shown), for example, then one of severalembodiments could take place.

[0068] In one such embodiment, the portions are not dynamically assignedto the new/third base station, but instead a new base station alwaysgets a fixed portion of bits to transmit. This works in a three-wayhandoff because the first two base stations are already transmitting allthe bits in the lower rate encoded bit stream, and the third basestation is merely used for redundancy. For instance, the third basestation can always transmit the even bits. In the above example, whereinbase station A is used for a three-way handoff, base station A transmitsthe even bits, while the existing base stations, B and C transmit theportion of bits that they were transmitting in the two-way handoffsituation (odd and even bits, respectively). This is done so that lessdynamic changes are needed to be made to the two channels alreadyinvolved in the call.

[0069] In another embodiment, the portions transmitted are dynamicallyreassigned to all base stations upon entering a three-way handoff. Inthis embodiment, the ids are all compared with each other, and the basestation with the lowest ID transmits one portion of bits while the otherbase stations transmit the other portion of bits. Thus, using basestations A, B, and C, again, the odd bits would be transmitted on basestation A, while the even bits would be transmitted on base stations Band C.

[0070] When communication from one of the base stations is terminated,such that either the remote station exits soft-handoff altogether, orswitches from a three-way handoff to a two-way handoff, the remotestation needs to know how the bits are being transmitted on theremaining base stations.

[0071] In one embodiment, when the remote station exits soft-handoff,the existing base station simply transmits a standard rate encoded bitstream, which the remote station decodes.

[0072] In one embodiment, when the remote station goes from a three-wayhandoff to a two-way handoff, the base stations continue transmittingthe portion of the encoded bit stream that they were transmittingbefore. In this embodiment, if they were both transmitting differentportions of the lower encoded bit stream (e.g., one base station wastransmitting odd bits and one was transmitting even bits), the remotestation combines them into a lower rate encoded bit stream. If, however,they were both transmitting the same portion of the lower rate encodedbit stream (e.g., both base stations transmitting even bits), then theremote station just decodes each received bit stream as a standard rateencoded bit streams. In such a case, as long as the remote stationremains in a two-way handoff, the bit streams received are handled asthey are in a conventional system.

[0073] In another embodiment, the portions transmitted are dynamicallyreassigned to all base stations upon going from a three-way handoff to atwo-way handoff. In this embodiment, the IDs are all compared with eachother, and the base station with the lowest ID transmits one portion ofbits while the other base stations transmit the other portion of bits.Using this embodiment allows the remote station in a two-way handoff tocombine the two bit streams into a lower rate encoded bit streamregardless of whether the two base stations in question weretransmitting the same bit streams while in a three-way handoff.

[0074] Remote station 38 can also use the method of the presentinvention at the boundary of cell or in a difficult situation such as afade even if it has not established communication links with multiplesectors. It is usually not desirable to use additional channels for allremote stations at all times because the additional channels consumecode channels and cells can run out of code channels. This reduces thecapacity of the communication system due to code limitations. Therefore,in one embodiment, additional code resources are allocated to remotestations that are using larger amounts of power due to poor channelconditions. In this way a cell can dynamically add and remove additionalcode channels for each remote station in order to maintain the codeconsumption and the power consumption in balance with each other.

[0075] Remote station 38, which is using much power because it is on theboundary of a cell, can use two channels 40, 42 transmitted from thesame sector S₁ when desirable. Each channel 40, 42 can contain the sameinformation bits encoded with a different code, thus decreasing theEb/No required for remote station 38. One of these channels is theprimary channel and one of these channels is the secondary channel.

[0076] When a remote station is not in handoff, such as is the case asdiagrammed with remote station 38, a base station can use a fundamentalchannel and a supplemental channel to transmit a lower encoded rate tothe remote station. In one embodiment, a methodology can be used suchthat one portion of bits from the lower encoded bit stream is alwaystransmitted on the primary channel and another portion of bits is alwaystransmitted on the supplemental channel (e.g., odd bits go to theprimary channel, while even bits go to the supplemental channel). Inanother embodiment, the base station can send a message to the remotestation informing it which portion of the lower encoded bit stream willbe transmitted on the primary channel, and which will be transmitted onthe supplemental channel.

[0077] It will be understood by one skilled in the art that theinvention is not limited to the above embodiments of methods oftransmission, nor the examples given above. In particular, the exampleof odd bits and even bits has been used throughout this application forconsistency. However, as described in reference to block 240 of FIG. 2,it is readily understood that other means of portioning the lower rateencoded bits can be used as well.

[0078] By decreasing the amount of power needed by remote stations thatare consuming a high level of power at any given moment, the presentembodiments serve to increase the number of users or the throughput thata telecommunications system can support at any given moment.

[0079]FIG. 6 is a block diagram showing a simplified illustration of aremote station. Digital demodulator 620, Walsh despreading unit 630,block deinterleaver 640, convolutional decoder 650, and controlprocessor 660 are coupled via a digital bus, and RF receiver 610 iscoupled to digital demodulator 620. In one embodiment, control processor660 can activate RF receiver 610 and digital demodulator 620 to receiveand process signals, and can deactivate them when in a power savingsmode, such as a slotted-paging mode. Likewise, in one embodiment,control processor 660 can selectively activate and deactivate blockdeinterleaver 640 and convolutional decoder 650. The RF receiver 610downconverts and digitizes RF signals, and provides the digitized signalto digital demodulator 620, which performs digital demodulation using PNdespreading techniques, further described in reference to FIG. 7. Thedigitally demodulated data is passed to Walsh despreading unit 630,which performs Walsh despreading techniques, further described inreference to FIG. 7, and produces at least one bit stream output. Forcoded channels, such as traffic channels, the bit stream output isprovided to block deinterleaver 640. In an embodiment that supports anuncoded auxiliary channel, such as a quick paging channel, which is anuncoded channel that uses on-off keying (OOK) modulated direct sequencespread spectrum, the bit stream output for the uncoded auxiliarychannels is provided from Walsh despreading unit 630 to controlprocessor 660 as an uncoded bit stream for further processing. In regardto coded channels, deinterleaver 640 deinterleaves the bit stream outputprovided by Walsh despreading unit 630, and provides a deinterleavedoutput stream to convolutional decoder 650. Convolutional decoder 650uses convolutional decoding techniques known in the art, such as Viterbidecoding or Turbo decoding, to attempt to correct bit errors thatoccurred to the informational bit stream that was transmitted over awireless environment. The convolutionally decoded bit stream is providedto control processor 660 for further processing.

[0080] In one embodiment, after receiving an indicator message, controlprocessor 660 instructs digital demodulator 620 and Walsh despreadingunit 630 to switch from a conventional mode of receiving data to a modeof the present embodiments in which data is received at a lower encodedrate across two channels. Likewise, control processor 660 can instructdigital demodulator 620 and Walsh despreading unit 630 to switch from amode of the present embodiments back to a standard data reception modeafter a predetermined time, or upon the receipt of another message froma base station instructing it to exit a mode of the present embodiments.

[0081] In one embodiment control processor 660 monitors the uncoded bitstream for indicator messages. In one embodiment control processor 660monitors the convolutionally decoded bit stream for indicator messages.

[0082] One skilled in the art will recognize that control processor 660may be implemented using field-programmable gate arrays (FPGA),programmable logic devices (PLD), digital signal processors (DSP), oneor more microprocessors, application specific integrated circuit (ASIC)or other devices capable of performing the functions described above.

[0083]FIG. 7 is a block diagram of a portion of digital demodulator 620and Walsh despreading unit 630 that can be used to receive data in adata reception mode of the present embodiments in which data is encodedusing a lower rate of encoding and is transmitted in portions over aprimary and secondary channel, wherein the transmissions of the primaryand secondary channel originate from the same base station.

[0084] PN despreader 710 is a complex PN despreader which performs PNdespreading, well known to one skilled in the art, on a digitized signalinput (from RF receiver 610) and produces an in-phase (I) and aquadrature-phase (Q) component of the PN despread signal, each of whichis provided to Walsh despreaders 720 and pilot filters 740 as inputsignals.

[0085] Walsh despreader 720 a multiplies the I 712 and the Q 714 inputsby a first Walsh code, which corresponds to the primary channel overwhich a first portion of a lower encoded rate bit stream wastransmitted, and sums the despread signal over one Walsh symbol, thusproducing as outputs Walsh despread I 722 a and Walsh despread Q 724 a.I 722 a and Q 724 a are provided as input to dot product 750 a.

[0086] Walsh despreader 720 b multiplies the I 712 and the Q 714 inputsby a first Walsh code, which corresponds to the primary channel overwhich a first portion of a lower encoded rate bit stream wastransmitted, and sums the despread signal over one Walsh symbol, thusproducing as outputs Walsh despread I 722 b and Walsh despread Q 724 b.I 722 b and Q 724 b are provided as input to dot product 750 b.

[0087] In one embodiment, pilot filters 740 are low pass filters thatare used to remove some of the noise from the received signal. Inalternate embodiments, pilot filters 740 consist of a Walsh despreader,similar to Walsh despreader 720 a but that despreads with a differentWalsh code, immediately followed by a low pass filter. As would beevident to one skilled in the art, I 742 and Q 744 are essentiallysmoothed-over estimates of the pilot signal. It would also be evident toone skilled in the art that the pilot signal could consist of a few bitsoccasionally inserted in either or both data streams, and extracted atthe output of Walsh despreaders 720 a and 720 b.

[0088] Dot products 750 function as what is known in the art as aconjugate complex product with the output of the pilot filter. Dotproducts 750 produce I and Q signal outputs that are estimates of the Iand Q values transmitted on the data channels. Such dot productapparatus are known to those skilled in the art. An exemplary embodimentof a dot product apparatus is illustrated in FIG. 8.

[0089] The outputs of dot product 750 a, namely I 752 a and Q 754 a, arethe I and Q components of the primary channel, and are provided tosymbol extractor 760 a. This will be called the primary symbolextractor, because it extracts the symbols corresponding to the primarychannel. The outputs of dot product 750 b, namely I 752 b and Q 754 b,are the I and Q components of the secondary channel, and are provided tosymbol extractor 760 b. This will be called the secondary symbolextractor, because it extracts the symbols corresponding to thesecondary channel.

[0090] Each symbol extractor 760 yields a series of symbols 762 basedupon the type of modulation used. In an exemplary embodiment in whichthe data was transmitted using QPSK modulation techniques, symbolextractor 760 yields two symbols 762 for each pair of I and Q inputs 752and 754. In another exemplary embodiment in which the data wastransmitted using Binary Phase Shift Keying (BPSK) modulationtechniques, symbol extractor 760 yields one symbol 762 for each pair ofI and Q inputs 752 and 754. Symbol extractor 760 provides these symbolsto summing unit 768. One skilled in the art will understand that inalternate embodiments that use other modulation techniques, symbolextractor 760 may be absent, in which case complex I and Q signals 752and 754 could be directly supplied to summing unit 768, or directlysupplied to MUX 770 (in an embodiment in which summing unit 768 is alsoabsent).

[0091] Two-channel finger 780 a is representative of a two-channelfinger that is used to track two channels (a primary and a secondary)from a single transmission signal generated by a single base station.Each two-channel finger 780 produces a primary and a secondary channeloutput. In an embodiment in which symbol extractors are present, theprimary channel output of a two-channel finger 780 is the output of theprimary symbol extractor (e.g., 762 a in FIG. 7), while the secondarychannel output is the output of the secondary symbol extractor (e.g.,762 b in FIG. 7). In an alternate embodiment in which symbol extractorsare not present, the primary channel output is the primary I and Qvalues (e.g., 752 a and 754 a), while the secondary channel output isthe secondary I and Q values (e.g., 752 b and 754 b).

[0092] To account for multi-path signals that can occur, the outputsfrom a plurality of two-channel fingers 780, each of which tracks thereceived signals at a slightly different PN offset or time delay, aresupplied to summing unit 768. Summing unit 768 sums the primary channeloutput produced by each two-channel finger 780, and provides it to MUX770. Additionally, summing unit 768 sums the secondary channel outputproduced by each two-channel finger 780, and provides the summed valueto MUX 770. As is known to one skilled in the art, a summer is used tocombine the output of multiple fingers in order to generate a betterestimate of the transmitted I and Q or symbol values. In someembodiments, summing unit 768 may also rescale the signals in order tokeep the signal within an acceptable dynamic range. The combinedestimate need not be generated prior to MUX 770, but can rather begenerated after MUX 770 in alternate embodiments. In an alternateembodiment, summing unit 768 is not present prior to MUX 770, in whichcase the primary channel outputs and secondary channel outputs from eachtwo-channel finger 780 are supplied directly to MUX 770.

[0093] In one embodiment, MUX 770 is a multiplexer that receives asinput primary channel data and secondary channel data from summing unit768, which MUX 770 arranges into a single symbol stream that is providedto block deinterleaver 640. The symbols are arranged in accordance withthe method used to transmit the data over the two channels. Forinstance, in an exemplary embodiment in which the odd bits aretransmitted on the primary channel and the even bits are transmitted onthe secondary channel, MUX 770 arranges the symbols 762 such that theestimate of the first received symbol corresponding to the primarychannel will be followed by the estimate of the first received symbolcorresponding to the secondary channel. In such an embodiment, thisprocess repeats, wherein another symbol is output corresponding to theprimary channel, followed by another symbol corresponding to thesecondary channel. The symbol stream yielded by MUX 770 is supplied toconvolutional decoder 650, further described in reference to FIG. 6.

[0094] An exemplary embodiment of dot product 750 is diagrammed in FIG.8. In FIG. 8, I 742 and I 722 are complex multiplied in complexmultiplier 810 a, while I 742 and Q 724 are complex multiplied incomplex multiplier 810 b. Likewise, Q 744 and Q 724 are complexmultiplied in complex multiplier 810 c, while Q 744 and I 722 arecomplex multiplied in complex multiplier 810 d. The output of complexmultiplier 810 a is then summed with the output of complex multiplier810 c in combiner 820 a, thus producing I 752. The output of complexmultiplier 810 d is subtracted from the output of complex multiplier 810b in combiner 820 b, thus producing Q 754.

[0095]FIG. 9 is a block diagram of a portion of digital demodulator 620and Walsh despreading unit 630 that can be used to receive data in adata reception mode of the present embodiments in which data is encodedusing a lower rate of encoding and is transmitted in portions over aprimary and secondary channel, wherein the transmissions of the primaryand secondary channel originate from different base stations, or whereinthe transmissions of the primary and secondary channel originate fromthe same base station (the latter provides an alternative to theapparatus described in reference to FIG. 7 in the case where the primaryand secondary channel originate from the same base station).

[0096] PN despreader 910 a is a complex PN despreader which performs PNdespreading, well known to one skilled in the art, on a digitized signalinput (from RF receiver 610)and produces an in-phase (I) and aquadrature-phase (Q) component of the PN despread signal, each of whichare provided to Walsh despreaders 920 and pilot filters 940 as inputsignals. PN despreader 910 a is used to decode a primary channel from afirst base station.

[0097] PN despreader 910 b is a complex despreader that functions likePN despreader 910 b. PN despreader 910 b behaves differently in that itis used to decode a secondary channel from a second base station. In oneembodiment PN despreader 910 b uses the same PN code for despreading asPN despreader 910 a, but at any given time PN despreader 910 b decodeswith a different portion of the PN code than does 910 a. In such anembodiment, the portion of the PN code used by each decoder for decodingat any given moment is determined by the PN offset associated with thebase station it is decoding a channel from. As the PN offset for thefirst base station is different from the PN offset of the second basestation in such an embodiment, the two PN despreaders 910 decode thereceived signal using different portions of the PN code at any givenmoment. In an alternate embodiment, PN despreader 910 a uses a differentPN code for despreading the received signal than does PN despreader 910b. In another alternate embodiment, for use in the case in which theprimary and secondary channel transmissions originate from the same basestation, one primary channel PN despreader 910 a and one secondarychannel PN despreader 910 b use the same PN code and the same PN offsetto decode the transmission; this can be used in lieu of a singletwo-channel finger 780 a, described in reference to FIG. 7.

[0098] Walsh despreader 920 a multiplies the I 912 a and the Q 914 ainputs by a first Walsh code, which corresponds to the primary channelover which a first portion of a lower encoded rate bit stream wastransmitted, and sums the despread signal over one Walsh symbol, thusproducing as outputs Walsh despread I 922 a and Walsh despread Q 924 a.I 922 a and Q 924 a are provided as input to dot product 950 a.

[0099] Walsh despreader 920 b multiplies the I 912 b and the Q 914 binputs by a second Walsh code, which corresponds to the secondarychannel over which a second portion of a lower encoded rate bit streamwas transmitted, and sums the despread signal over one Walsh symbol,thus producing as outputs Walsh despread I 922 b and Walsh despread Q924 b. I 922 b and Q 924 b are provided as input to dot product 950 b.

[0100] In one embodiment, pilot filters 940 are low pass filters thatare used to remove some of the noise from the received signal. Inalternate embodiments, pilot filters 940 consist of a Walsh despreader,similar to Walsh despreader 920 a but despreading a different Walshcode, immediately followed by a low pass filter. As would be evident toone skilled in the art, I 942 a and Q 944 a are essentiallysmoothed-over estimates of the pilot signal of the first base station.It would also be evident to one skilled in the art that the pilot signalof the first base station could consist of a few bits occasionallyinserted in either or both data streams, and extracted at the output ofWalsh despreaders 920 a. Likewise, as would be evident to one skilled inthe art, I 942 b and Q 944 b are essentially smoothed-over estimates ofthe pilot signal of the second base station. It would also be evident toone skilled in the art that the pilot signal of the second base stationcould consist of a few bits occasionally inserted in either or both datastreams, and extracted at the output of Walsh despreaders 920 b.

[0101] Dot products 950 function as what is known in the art as aconjugate complex product with the output of the pilot filter. Dotproducts 950 produce I and Q signal outputs that are750 estimates of theI and Q values transmitted on the data channels. Such dot productapparatus are known to those skilled in the art. An exemplary embodimentof a dot product apparatus is illustrated in FIG. 8.

[0102] The outputs of dot product 950 a, namely I 952 a and Q 954 a, arethe I and Q components of the primary channel, and are provided tosymbol extractor 960 a. This will be called the primary symbolextractor, because it extracts the symbols corresponding to the primarychannel. The outputs of dot product 950 b, namely I 952 b and Q 954 b,are the I and Q components of the secondary channel, and are provided tosymbol extractor 960 b. This will be called the secondary symbolextractor, because it extracts the symbols corresponding to thesecondary channel.

[0103] Each symbol extractor 960 yields a series of symbols 962 basedupon the type of modulation used. In an exemplary embodiment in whichthe data was transmitted using QPSK modulation techniques, symbolextractor 960 yields two symbols 962 for each pair of I and Q inputs 952and 954. In another exemplary embodiment in which the data wastransmitted using Binary Phase Shift Keying (BPSK) modulationtechniques, symbol extractor 960 yields one symbol 962 for each pair ofI and Q inputs 952 and 954. Symbol extractor 960 provides these symbolsto summing unit 968. One skilled in the art will understand that inalternate embodiments that use other modulation techniques, symbolextractor 960 may be absent, in which case complex I and Q signals 952would be directly supplied to summing unit 968, or directly supplied toMUX 970 (in an embodiment in which summing unit 968 is also absent).

[0104] Finger 980 a is representative of a finger that is used to tracka single channel (a primary one) from a single transmission signalgenerated by a single base station. Each finger 980 tracks either aprimary channel or a secondary channel and produces a primary or asecondary channel output accordingly. For instance, finger 980 a tracksa primary channel and therefore produces a primary channel output, whilefinger 980 b tracks a secondary channel and therefore produces asecondary channel output. In an embodiment in which symbol extractorsare present, the primary channel output of a finger 980 that tracks aprimary channel is the output of the primary symbol extractor (e.g., 962a in FIG. 9), while the secondary channel output of a finger 980 thattracks a secondary channel is the output of the secondary symbolextractor (e.g., 962 b in FIG. 9). In an alternate embodiment in whichsymbol extractors are not present, the primary channel output is theprimary I and Q values (e.g., 952 a and 954 a), while the secondarychannel output is the secondary I and Q values (e.g., 952 b and 954 b).

[0105] To account for multi-path signals that can occur, the outputsfrom a plurality of fingers 980, each which track a primary or secondaryreceived signals at a slightly different PN offset or time delay, aresupplied to summing unit 968. Summing unit 968 sums the primary channeloutput produced by each primary channel finger 980, and provides it toMUX 970. Additionally, summing unit 968 sums the secondary channeloutput produced by each secondary channel finger 980, and provides thesummed value to MUX 770. As is known to one skilled in the art, a summeris used to sum the output of multiple fingers in order to generate abetter estimate of the transmitted I and Q symbol values. In someembodiments, summing unit 968 may also rescale the signals in order tokeep the signal within an acceptable dynamic range. The combinedestimate need not be generated prior to MUX 970, but can rather begenerated after MUX 970 in alternate embodiments. In an alternateembodiment, summing unit 968 is not present prior to MUX 970, in whichcase the primary channel outputs and secondary channel outputs from eachprimary channel finger 980 and secondary finger 980, respectively, aresupplied directly to MUX 970.

[0106] In one embodiment, MUX 970 is a multiplexer that receives asinput primary channel data and secondary channel data from summing unit968, which MUX 970 arranges into a single symbol stream that is providedto block deinterleaver 640. The symbols are arranged in accordance withthe method used to transmit the data over the two channels. Forinstance, in an exemplary embodiment in which the odd bits aretransmitted on the primary channel and the even bits are transmitted onthe secondary channel, MUX 970 arranges the symbols 962 such that theestimate of the first received symbol corresponding to the primarychannel will be followed by the estimate of the first received symbolcorresponding to the secondary channel. In such an embodiment, thisprocess repeats, wherein another symbol is output corresponding to theprimary channel, followed by another symbol corresponding to thesecondary channel. The symbol stream yielded by MUX 970 is supplied toconvolutional decoder 650, further described in reference to FIG. 6.

[0107] The group of modules located in each box 980 is representative ofa finger used to track a signal from a signal base station, withouttaking into account multi-path signals that might be received from eachbase station as well. Although, for the sake of simplicity, multiplefingers used to track multipath signals is are shown in FIG. 9, oneskilled in the art will understand that to account for a multi-pathenvironment more fingers 980 with different PN offsets can be added totrack multiple multi-path signals from one or more base stations in amulti-path environment.

[0108] The previous description of the embodiments is provided to enablea person skilled in the art to make or use the present invention. Thevarious modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments without the use of the inventivefaculty. Additionally, the various methods taught herein can be combinedwith each other in any manner without the use of the inventive faculty.Thus, the present invention is not intended to be limited to theembodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed.

1. A method for transmitting an information bit stream, comprising:receiving an information bit stream to be transmitted; forming at leasta first transmission signal and a second transmission signal if atransmit power level value of the information bit stream is above apredetermined threshold, wherein each of said first and secondtransmission signals include bits selected from the information bitstream; and transmitting each of the first and second transmissionsignals over a respective one of at least two transmission links.
 2. Themethod of claim 1, further comprising: transmitting the information bitstream over a single transmission link providing that the transmit powerlevel value of the information bit stream is below the predeterminedthreshold.
 3. The method of claim 1, wherein the at least twotransmission links are formed between a remote station and a single basestation.
 4. The method of claim 3, wherein the at least two transmissionlinks are established over separate transmission channels.
 5. The methodof claim 1, wherein the at least two transmission links are formedbetween a remote station and a plurality of base stations.
 6. The methodof claim 5, wherein the transmission signal of each of the at least twotransmission links are mixed with the same Walsh code.
 7. The method ofclaim 5, wherein the remote station is in soft handoff between at leasttwo of the plurality of base stations.
 8. The method of claim 3, whereinthe remote station is in softer handoff within the single base station.9. The method of claim 1, further comprising determining whether anumber of available spreading codes is above a predetermined level. 10.The method of claim 1, further comprising encoding the information bitstream using a rate R=1/n code, wherein n is an integer value indicatinga number of output bits.
 11. The method of claim 10, wherein forming theat least first transmission signal and second transmission signalcomprises assigning alternating bits of the information bit stream tothe first transmission signal and second transmission signal.
 12. Themethod of claim 1, further comprising generating a message indicatinghow the first transmission signal and the second transmission signalwere formed using the bits selected from the information bit stream. 13.An apparatus for transmitting an information bit stream, comprising:means for receiving an information bit stream to be transmitted; meansfor forming at least a first transmission signal and a secondtransmission signal if a transmit power level value of the informationbit stream is above a predetermined threshold, wherein each of saidfirst and second transmission signals include bits selected from theinformation bit stream; and means for transmitting each of the first andsecond transmission signals over a respective one of at least twotransmission links.
 14. The apparatus of claim 13, further comprising:means for transmitting the information bit stream over a singletransmission link providing that the transmit power level value of theinformation bit stream is below the predetermined threshold.
 15. Theapparatus of claim 13, wherein the at least two transmission links areformed between a remote station and a single base station.
 16. Theapparatus of claim 15, wherein the at least two transmission links areestablished over separate transmission channels.
 17. The apparatus ofclaim 13, wherein the at least two transmission links are formed betweena remote station and a plurality of base stations.
 18. The apparatus ofclaim 17, wherein the transmission signal of each of the at least twotransmission links are mixed with the same Walsh code.
 19. The apparatusof claim 17, wherein the remote station is in soft handoff between atleast two of the plurality of base stations.
 20. The apparatus of claim15, wherein the remote station is in softer handoff within the singlebase station.
 21. The apparatus of claim 13, further comprising meansfor determining whether a number of available spreading codes is above apredetermined level.
 22. The apparatus of claim 13, further comprisingmeans for encoding the information bit stream using a rate R=1/n code,wherein n is an integer value indicating a number of output bits. 23.The apparatus of claim 22, wherein the means for forming the at leastfirst transmission signal and second transmission signal comprises meansfor assigning alternating bits of the information bit stream to thefirst transmission signal and second transmission signal.
 24. Theapparatus of claim 13, further comprising means for generating a messageindicating how the at least first transmission signal and the secondtransmission signal are formed using the bits selected from theinformation bit stream.